Process for producing a fused reducing bath for descaling



Dec. 20, 1966 M. MEKJEAN ETAL PROCESS FOR PRODUCING A FUSED REDUCINGBATH FOR DESCALING Filed Aug. 50. 1961 3 Sheets-Shed; 1

Dec. 20, 1966 MEKJEAN ET AL.

PROCESS FOR PRODUCING A FUSE'D REDUCING BATH FOR DESCALING I Filed Aug.50. 1961 3 Sheets-Sheet 2 m Q w l I t -|m\:I\\1 |1 ll i 1 1| ill! I I W1111111 I11! :mrlll 0? WM I I IHW HI I I1 I I M l h WMMHHHH .H l l l z W1% M m l N Dec. 20, 1966 MEKJEAN ET AL PROCESS FOR PRODUCING A FUSEDREDUCING BATH FOR DESCALING Filed Aug. 30. 1961 3 Sheets-Sheet 3 UnitedStates Patent PROCESS FDR PRODUCING A F-USED REDUCING BATH FOR DESCALINGMatthew Mekjean, Niagara Falls, and Charles A. Strack,

Lewiston, N.Y., assignors to Hooker Chemical Corporation, Niagara Falls,N.Y., a corporation of New York Filed Aug. 30, 1951, Ser. No. 134,967 6Claims. (Cl. 20461) This invention relates to the art of removingoxygencontaining heat scale from metals. More specifically, theinventive concept herein defined resides in a unique type of reducingdescaling fused salt bath.

Some descaling difliculties have been encountered because of thechemically resistant nature of the heat scale developed on certain metalspecies in the usual annealing and 'hot rolling procedures used inproduction. vHigh nickel steels, for example, have presented variousdescaling problems by presently existing molten salt systems. Thepresent invention provides an economical alkalimetal hydroxide baseddescaling system particularly adapted for use in the descaling of nickelsteels, high nickel alloys, stainless steels and many other metals andalloys. It has been found that presently commercially used reducingdescaling systems, while somewhat eifective and desirable, presentcorrosion problems both on the bath containing pot, gas-fired heatingtubes, immersion rolls and other component elements of the equipment. Afurther apparent drawback of the presently used reducing descaling bathsis the ever present danger of violent reactions caused by the constantaddition of various chemicals to the system. To be commerciallydesirable, a system of this type must not be effective as such, but mustbe economical to operate, while maintaining a high degree of safety. Thesystem of this invention electrolytically creates and maintains asubstantially constant source of reducing chemicals in the bath whileproviding the bonus effect of a highly desirable degree of safety.

The present invention is adaptable both to batch descaling units and tocontinuous descaling of strip. The trend in the primary metal industryis more and more toward automation, away from batch handling, andwherever possible and feasible, to produce the bulk of the products ofthe rolling mills in the form of strip. The rolling process, both onsheet products and strip, Workha-rdens the metal, which is then usuallyannealed or softened in a heat-treating step which leaves the surface ofthe metal covered with a heat scale which is difiicultly soluble in acidpickling baths. It is at this point, after annealing, that the fusedsalt reducing descaling bath of the present invention is mosteffectively utilized. In strip lines, the descaling bath is located justbeyond the exit of the annealing furnace. The hot, annealed stripcontinuously passes directly from the annealing furnace into thedescaling bath, where it is held submersed by special immersion rolls.The strip passes over exit rolls, then through a water quench tank, andspecial rolls lead it through one or more acid pickling tanks, sprayrinses, air dryers, and past the inspection stations and the descaledmetal is finally rolled into large coils.

The present invention provides a very versatile electrochemical process,where the proper control of direct current in suitable equipmentproduces and maintains an equilibrium composition of the reducingchemicals that effectively descale the metals and alloys of interest.While the electric current provided in this system does not directlyparticipate in the descaling ope-ration, it is vital and necessary toinsure the production of the reducing agents which are responsible forthe deoxidatio-n of heat scales on metals. The typical system of thisin- Patented Dec. 20, 1966 vention initially comprises a Na SO -NaOHmelt maintained at a predetermined temperature in a melt pot. Immersedin the pot is a cathode means, an anode means, an anolyte and cath'olytecompartment determining structures. The initial composition of the bathis usually a molten Na SO -NaOH mixture. The preferred compositioncomprises from six (6.0) percent Na SO to eighteen (18.0) percent N-a SOthe remainder substantially anhydrous NaOH. It would not however beconsidered without this invention to alter the amounts of either NaOH orthe Na SO in the system. It has been found for example that any amountvof Na SO greater than three (3.0) percent may be utilized in thisinvention, although as mentioned above the preferred compositioncomprises from six (6.0) to eighteen (18.0) percent Na SO When thecurrent is introduced into the system, the Na SO is progressivelyreduced to a complexity of ions which will be more clearly defined inthe ensuing discussion. The Na SO itself is neither reducing noroxidizing, thus is not the descaling medium as such. However, thereducing ions that are electrochemically formed when the current isintroduced into the Na SO NaOH molten bath are highly desirablereducing-descaling agents.

Although the complexity of the chemical reactions that take place inthis system have not been completely verified, it is believed that thebelow defined reactions occur. Electrolyte reduction of sodium sulfateyields a number of reducing agents in the melt, which, in turn, are alsosubjected to electrolytic reduction to be them-selves further reduced asfollows:

Apparent Valence Na SO Sulfate +6 +0 l-o Disproportionation M12503Sulfite +1;

Pyrosulfite Na O+Na S O5 na s o Dithionite +3 M25203 Thiesulfate N825Sulfide -2 elec. reduction NaaSzOs *S Nil-23204 IAOQT At the cathode theS 0 takes on two electrons to create S O -f-O' The oxygen ion migratesto the anode where it loses two electrons to become 0 or molecular xygengas which escapes from the system. The general verall reaction thuswould be electrolytic reduction NazS2O5 azS204 %02 incompassed in thisbroad concept of the reduction of he Na SO -NaoH mixture to a number ofreducing agents It compounds, is also the further teaching of a possiblelath to be used in commercial manufacturing of these relucing agents orcompounds or their acid forms.

The Na SO in the initial molten composition is in lectrochemicalcombination with and is electrolytically educed to the reducingsulfites, dithionites, thiosulfates, iyrosulfites, and sulfides amongothers. These reducing igents combine with the oxides of the scale onwork- :ieces to be re-oxidized to the higher oxygen level, which henagain is electrolytically reduced; thus, a continuous)XldflllOl'l-l'fidllCllOll cycle takes place without any subtantial needfor re-supplying the system externally with tdditional chemicals. Afurther effect is accomplished by hese ions in the transitory state; forexample, Na SO vhile being an effective reducing agent, is also highlycor- 'osive in, the system. For example, the Na SO that is 'ormed, whilesupplying (together with the other ions Formed) a highly desirabledescaling bath, is converted to he Na SO u-pon descaling since it willhave a tendency o rob or absorb oxygen from the oxide scale. The cor-.OSlV6 effect of the Na SO thus is kept at a minimum vhile the descalingefforts of the Na SO are utilized together with the combined descalingeffects of the other ons formed. It is believed that the descalingoperation of his invention functions in the following manner: Using 51218 Na SO Na S O- as typical examples of the relucing agents in thissystem that are re-oxidized by the scale, the following are consideredillustrative of the :hemistry involved in the descaling operation; anymetal :0 be descaled will be indicated below by the symbol Me. Anhydrousalkali-metal hydroxide is the solvent:

The descaling reactions re-create the higher oxidation states (highersulfur valences) of the alkali-metal sulfuroxygen salts, which in turn,are electrolytically reduced to repeat the cycle. The overall effect isto remove combined oxygen from the scale on workpieces of metal by thechemical reducing agents, and to release this as molecular oxygen gas bythe electrolytic reduction of the oxidized reducing agents. Thus, thecycle is repeated ad infinitum; regeneration of the reducing agentselectrolytically, and descaling of workpieces by chemical reductionoftheir oxide scales.

The elements of the reducing bath system of this invention include afused, substantially anhydrous molten salt or electrolyte, a directcurrent electrical source, a cell converter (Recyclotron) comprising incombination a cathode means, an anode means, and a diaphragm means, acontainer pot, a passivating circuit, and a floating cover, which may beoptionally used.

Utilization of the passivating circuit in the present system is aspecially-devised and unique application of direct electrical current.Laboratory tests have demonstrated that otherwise soluble metals in thefused salt can be so passivated 'by this technique that the useful lifeof equipment can be extended ten (10), twenty (20) and even thirty (30)times normal. In its simplest concept, the passivating techniqueinvolves an anomaly: to use positive electricity in the presence ofstrong reducing agents, yet passivating the elements maintained positivewithout destroying or minimizing the reducing nature of the fused salt.Another unique factor is that this passivation technique is particularlyeffective in the substantially anhydrous molten salt mixture, and isless effective when water is present in the melt. In practice, thoseelements of the present system requiring passivation (such as the potmean-s, diaphragm means, housing means, thermocouple probes, sludgepans, bafiles, or other specialized equipment such as rolls, agitators,pumps, etc.) are connected in parallel to the positive pole, for exampleof a rectifier. The negative pole is connected to either the recyclotroncathode or to a special electrode contacting the fused salt. The currentin this separate, superimposed passivating circuit is adjusted withinthe range from about one-hundredth to a maximum of about one-tenth ofthe recyclotron current, and is somewhat dependent on the total area ofequipment being passivated.

A floating cover of light particles may be optionally used on thesurface of the catholyte. The purpose of such a cover would be toincrease the efiiciency of the reducing bath by preventing unnecessaryoxidation of the active re ducing agents with the oxygen of theatmosphere. A secondary advantage would be realized in conserving aportion of the radiant heat normally lost from the open surface of thebath. Such a floating cover on the fused salt should consist of acomposite of large and small particles ranging approximately from one(1) to thirty-two (32) mesh. Such particles, whose density is less thanthat of the molten salt, could conveniently consist of porous materialssubstantially stable in the system.

Initially, the molten salt as above discussed preferably comprises NaOHand Na SO in the ratio of about from six (6.0) percent to eighteen(18.0) percent Na SO to ninety-four (94.0) percent to eighty-two (82.0)percent NaOH. This molten mixture is substantially anhydrous and ismaintained preferably at temperatures from six hundred (600) degreesFahrenheit to one thousand (1000) degrees Fahrenheit. Of course, anyelevated tem perature below the boiling point of the molten mixture maybe employed depending on the desired result. Any suitable type ofheating may be used depending on the conditions and techniques involved.The NaOH used is preferably technical grade caustic soda (essentiallyanhydrous) having mixed therewith from six (6) to eighteen (18.0)percent by weight of the total dry components of Na SO When this mediumis electrolyzed, first the elements of water are decomposed to oxygen atthe anode and hydrogen at the cathode, leaving a substantially anhydroussalt in the melt (at temperatures ranging from about six hundred (600)to about one thousand (1000) degrees Fahrenheit, the preferredtemperature being from about seven hundred (700) to about nine hundred(900) degrees Fahrenheit). When completely anhydrous, the continuedelectrolysis causes oxygen gas to be liberated at the anode, andreduction of the sulfate occurs at the cathode to yield reducing agentsas above discussed (such as sodium sulfite, sodium thiosulfate, etc.).

It would not be considered without the scope of this invention toprovide (at greater expense) an initial mixture of components such asNaOHNa SO Na SO Na S O Na S O -Na S O Na S in any combination of NaOHwith one, two, three, four, five, or all six. The use of NaHS and evenelemental sulfur, initially, will immediately react with NaOH to createsome of the alkali metal sulfur-oxygen compounds listed, and without thereducing electric current, lW-Ollld eventually convert completely to NaSO the stable form.

Technical grade caustic soda is normally preferred since it iscommercially available at a relatively low cost. Hence, when technicalgrade caustic soda is employed, small amounts of impurities normallyassociated therewith are present in the bath, i.e., around three (3)percent cumulatively by weight of sodium chloride, sodium carbonate,etc. based on the total composition. It will be noted. that in use thealkali hydroxide-based molten salt bath slowly absorbs carbon dioxidefrom the atmosphere and converts some of the hydroxide to alkalicarbonate. Another source of carbon dioxide in the proximity of the bathwould be the exhausts of gas or oil-fired. heating tubes for maintainingthe salt in the molten state. This conversion of alkali metal hydroxideto alkali metal carbonate in no way adversely affects the utility of thesalt bath; in fact, carbonate below thirty (30) percent increases thefluidity of the salt due to a lowering of the melting point of themixture.

The melt also has a remarkable capacity for holding a number ofcontaminants, such as most metallic cations, for example, Cu, Ni, Cr,Sn+ Pb+ Zn, Ti+ Ag+, Fe+ Co+ Mo+ W+ B a++ Ca+ and V+ These would, ascontaminants, be present usually in low concentrations and obtained, inmost cases from the metallic scales being reduced by the catholyte. TheNaOH will act as a solvent for these contaminants.

The sources of direct electric current in this system are preferablyobtained by metallic rectifiers such as selenium, germanium or silicon.However, motor generators and batteries with their limitations, may beutilized especially in smaller systems. The direct current requirementsof this system are in the approximate maximum range of about fivehundred (500) amperes per ton of salt during start-ups, or duringperiods of increased demand, and approximately two hundred and fifty(250) amperes per ton minimum for normal operation. The actual operatinglevel demand would determine the operating current requirements. Theactual current demand in each particular installation would probablyvary, however, with the efficiency of the equipment and type of scalebeing reduced, in conjunction with the particular analysis of the salt.It is most desirable for the system to operate at a maximum of about six(6) volts for personnel safety, as well as for economical power costs.

It is therefore an object of the present invention to provide a metaldescaling system which will electrolytically maintain a substantiallyconstant source of reducing chemicals within the reducing bath whileproviding the further advantage of a highly desirable degree of safetyto operating personnel.

Another object of this invention is to provide a metal descalingcomposition which initially comprises (alkali) sodium sulfate in sodiumhydroxide, which is electrolytically reduced to produce and maintain anumber of reducing agents such as sulfite, pyrosulfite, dithionite,thiosulfate, sulfide and the like.

A further object of this invention is to provide a novel structure whichwill maintain the above-mentioned descaling compositions.

A still further object of this invention is to provide a novel cathodemeans which is particularly adapted for use in the present system.

A still further object of this invention is to provide anelectrochemical process in which the proper control of direct currentyields the reducing chemicals which effectively descale the metals andalloys of interest.

Other objects of this invention will become apparent from a furtherreading of this disclosure.

The invention will be further defined in relation to the accompanyingdrawings and following examples. It is to be understood however, thatthe drawings and examples in the following discussion are given merelyto illustrate the invention, and are not by any means to be taken aslimiting the invention to the particulars herein defined.

FIGURE I discloses a modification of the reducing salt bath system ofthis invention. FIGURE 11 illustrates a preferred embodiment of thereducing bath of this invention. FIGURE III illustrates a preferred cellstructure included in the Recyclotron system of this invention.

Referring first to FIGURE I, the reducing system 1 comprises a metal pot2. The salt or a molten descaling composition 17 is restricted orcontained in pot 2. Most of the commercially used pots are comprised ofsteel. The material of constmction of the pot is of utmost importance inthe present invention, since it should have a long life and beessentially inert chemically. Immersed in salt 17 is an anode means 3, acathode means 4, and

a diaphragm means 7. The diaphragm means bisects the internal area ofpot 2, thereby forming an anode compartment 5, and a cathode compartment6, although the compartments do not have to be the same size. When anodemeans 3 and cathode means 4 are connected to an electrical source ofdirect current, the ions in the fused salt carry the current between theinert electrodes, forming a number of reducing ions at the cathode. Theoxygen ion formed is attracted to the anode, passes through diaphragmmeans 17 to the anode where it loses its electrons, and is released asoxygen gas. When a direct current flows between the electrodes, rangingfrom 0.5 to 3.5 amperes per square inch of cathode surface at animpressed ranging from one (1.0) to 7.5 volts, a reducing bath iscreated in the catholyte. The metal to be descaled is generally simplyimmersed in the molten catholyte or cathode compartment for thedescaling openation. However, eventually, on continuous operation, boththe anode and cathode compartments 5 and 6 become effective for thedescaling of steels or other metals and analysis of the anolyte andcatholyte reveals the presence of the reducing agents in both. Althoughit is conceivable that a cell may be so constructed that might obviatethe need for a diaphragm, it would probably be more complicated than toactually use one to assist in separating the anode product from theproducts of the cathode. The use of the diaphragm between anode 3 andcathode 4 permits miniaturization of the reducing bath generatingsystem, which then allows the bulk of the pot volume to be utilized asan active working area for the descaling of metals. The more perfect theseparation of the products of the electrodes from each other, the higherthe electrical efiiciency of the system. Because of the dissolution ofmost diaphragm materials tested, only passivated iron, nickel orzirconium have proven satisfactory as materials of construction for thediaphragm. Especially designed and fabricated screens and porous orperforated plates have been successfully used; however, any specificallyconstructed diaphragm particularly suitable for the purpose for which itis designed needs to be protected by the passivating circuit.

The actual reduction of the sulfate essentially occurs at the inertcathode, whereby the reducing chemicals are liberated. The design, size,current density, voltage, current flow, and materials of constructionare all important for the greatest efficiency of this system. Naturally,the composition of the salt, basically, has determined the formervariables. The best cathode material of construction is copper and someof its alloys, due to its electrical efficiency, fairly low cost andrelatively long life. It must be remembered that all cathode materialseventually dissolve. Other metals exhibiting long life as cathodematerials are nickel, silver, zirconium and molybdenum. Economicconsiderations probably would restrict the choice of the cathodematerial to copper, nickel, or their alloys. Special precautions arenecessary in the present system to insure maximum cathode life. Thiswill be defined in greater detail in the ensuing discussion.

At the anode means 3, oxygen in the melt, obtained from the metal oxidescales, by absorption by the reducing agents of oxygen from theatmosphere, or from anions containing oxygen, is liberated as a gas,removing it from the system. This leaves the melt somewhat oxygen-shy,or hungry for more oxygen. The object is to supply the oxygen by thechemical reduction of scale on metallic workpieces. Iron, nickel andcobalt and their alloys with each other are the anode materials thathave demonstrated the longest life, and economic considerations wouldindicate a preferance for iron or nickel, or an iron-nickel alloy forthe composition most suitable for the anode. For fine laboratory workand scientific measurements, platinum may be utilized as an anode, butas a cathode, platinum dissolves.

Pot 2 is generally constructed of steel; however, laboratory use wouldindicate a preference for nickel. The

naterial of construction for the pot is of utmost imporance, since itshould have long life and be essentially inert :hemically. Since thecommercial preference is steel, the )16561112 system was designed forparticular use with the netal steel-type pot. The cell structuretherefore of FIG- JR'E I produces reducing compounds in the melt tocreate he reducing bath. The simplest cell is composed as illus- ;ratedof the pot itself, separated into two compartments )y a dividingdiaphragm, one the anode compartment con- ;aining the anode, and theother a cathode compartment :ontaining the cathode. The electrolyte, ormolten (fused) salt in this case, completes a working cell ready forapplication of the electric current between the electrodes. When thecurrent flows, the salt in the anode :ompartment becomes the anolyte.The salt in the cathode compartment therefore becomes the catholyte. Inoperation, the catholyte is chemically reducing in nature, and becomesthe working area of the bath. It is Within the catholyte that workpiecesof metal are exposed for the reduction of their oxide scales, or wherethe scale is conditioned or converted. In commercial baths of this type,it would be obviously advantageous to make the anode compartmentrelatively small and the cathode compartment relatively lange. In orderto insure a reasonable life of the pot and the diaphragm in this system,they should be connected to the passivating circuit.

FIGURE II. A preferred embodiment of this invention is illustrated. Thisembodiment provides a metal pot 9, having therein a reductive housingmeans. This reductive, which we will identify in the ensuing discussionas a Recyclotron structure, comprises a steel housing 10 containing theanode 12 and a diaphragm means 11. This housing then would determine theanode compartment in the anolyte, and a cathode compartment in thecatholyte. The cathode is usually separately situated in its positionopposite the diaphragm of the housing and is electrically insulated fromeverything in the system. The main area of the pot, therefore, in whichthe cathode is located, becomes the cathode compartment, the salt withinit becomes the catholyte, and therefore becomes the working area of thisreducing bath. For this system to function safely, therefore, and toinsure the safety of equipment, the housing, the diaphragm, the pot, thesludge pan, and other necessary accessories, are connected to thepassivating circuit. The cell construction illustrated in FIGURE II ispreferred over that of FIGURE 1, in that the structure of FIGURE I hascertain limitations. The cell structure of FIGURE 1 would probablyrequire modification of presently-used commercially existing systems. Itwould economically be more desirable to use the system illustrated inFIGURE II, in that the recyclotron 10 can be merely lowered into acommercially-used pot or bath. It would be self-contained, and whenconnected to the proper electrical source, would automatically create areducing, descaling bath in situ. The size or number of theserecyclotrons would depend upon the size of the bath and the applicationof the bath. In most cases, it is assumed that a special design would beutilized; in other words, the standard design may be modified to suitthe particular needs.

FIGURE III illustrates an enlarged view of a recyclotron of this system.The recyclotron of this system comprises in combination a steel housingmeans 10, which encloses the anode means 12. On the lower portion of thecombination bathe-diaphragm means 11 is positioned perforated diaphragmmeans 2-1. Outside of housing 1i? and immediately adjacent the diaphragmmeans 21 and parallel thereto, is positioned a cathode means 16. Therehas been a considerable amount of difficulty encountered in preventingthe corrosion of the electrical cathode lead 18, to the submergedcathode means 16. One main difficulty in the corrosion of the electricallead 18 occurs at the air-liquid interface where corrosion most readilyoccurs. Once the electrical lead 18 to the cathode fails because ofcorrosion, the entire cathode means 16 itself then becomes useless tothe system. -It has been found that the life of the electrical lead '18which connects the cathode 16 to the source of current has been greatlyincreased by the incorporation of an outer zirconium sheath 17substantially completely enclosing the electrical lead 18. The zirconiumis substantially inert in the system and does not hinder or harm thesystem of the operation of the present reducing bath. The zirconiumsheath 17 concentrically encloses electrical lead 1-8, therebysubstantially completely preventing any corrosion of the cathodeelectrical lead 18. By using a protective system of this nature, notonly is the life of cathode 16 extended, but also the life of the entiresystem is extended. The reducing system (recyclotron), there-bycomprises in combination a cathode .16, a cathode lead 18, a cathodelead sheath 17, an anode 12, anode lead 20, a housing 10, and acombination bathe-diaphragm means 111. The cathode bus bar 19 supportscathode lead .18, which is concentrically enclosed by zirconium sheath17. Vertically suspended on cathode lead 18 is cathode means 16. Anodemeans .12 is suspended within the internal portion of housing I10.

A further preferred embodiment (not illustrated herein) of therecyclotron of this invention comprises a structure having an anodemeans, a diaphragm means, a cathode means, an anode electrical lead, acathode electrical lead, and a source of current, said diaphragm meansconcentrically substantially enclosing said anode means, said cathodemeans concentrically substantially enclosing said diaphragm means, a topclosure means positioned in a substantially gas tight manner betweensaid anode means and said diaphragm means, and the upper areaintermediate said diaphragm means and said cathode means defining a gaspassage means extending from the internal portion of said recyclotnon tothe atmosphere, said electrode electrical leads supplying electricalcurrent to said electrodes from said source of current. This embodimentis preferred since it also may be immersed in presently existing pots,while having the bonus effects of occupying a minimum amount of space athigh electrical efiiciency,

The following examples further define the specifics of this invention.The metals descaled in the following examples were primarily high nickelsteel and typical stainless steels. However, other types of metalstested under proper descaling conditions yielded excellent results. Someof the other metals which may be descaied in the present system arestraight-chrome stainless steels, chrome-nickel stainless steels,silicon steels, titanium and its alloys, mild steels (low carbonsteels), nickel steels, copper and its alloys such as bronze, brass andso forth, molybdenum and its alloys, and such heat resistant andcorrosion resistant nickel-based alloys with molybdenum and iron, withsilicon; and with nickel-chromium alloys with molybdenum and tungsten,or with molybdenum and iron, or with cobalt and iron. We haveundoubtedly not exhausted the number of diiferent alloys and metals thatcan be effectively descaled in the present system, but this list wouldbe restricted essentially to those metals and alloys which aresubstantially unreactive in the salt, and to those Whose meltingpointsare above the operating temperature of the descaling medium.

Examples 1 through 14 inclusive have to do exclusively with a series ofdescaling tests performed on a nickelsteel alloy undersuccessively-varied conditions of the descaling system in order toestablish the ideal operating conditions. The particular nickel-steelused in these examples will be identified as 908, which has a typical oraverage alloy composition of the major elements of 77.2 percent nickel,4.8 percent copper, 1.5 percent chromium and 14.9 percent iron. A largesheet of scaled 908 nickel steel was cut into standard panels of two (2)inches Wide by three (3) inches long, and each was given a numberidentification.

Examples 15 through 20 illustrate the effectiveness of the electrolyzedsalt to descale various stainless steels in catholyte or anolyte in thetemperature range from EXAMPLE 1 A salt composition A, comprising 91.5percent technical grade sodium hydroxide and 8.5 percent anhydroussodium sulfate, based on the total dry weight of the components, wascharged into an experimental steel pot fitted with slots for positioningand holding the diaphragm screen. The diaphragm screen bisected the potinto two compartments of equal size, the one comprising the anodecompartment containing a nickel anode, and the other comprising thecathode compartment containing a copper cathode. The total charge to thepot was one hundred and thirty (130) pounds of molten salt-electrolyte.The electrodes were so positioned that they Were opposite each other,with the diaphragm substantially centrally located between them. Theinitial distance between parallel faces of the electrodes was eight andone-half (8 /2) inches. The temperature of the melt was held in thisinstance at seven hundred and twenty-one (721) degrees Fahrenheit. Thepassivating circuit was connected to the pot and to the diaphragmscreen, and was held at two (2) amperes at two (2) volts throughoutthese tests. The reducing current in the Recyclotron was set for forty(40) amperes at 4.1 volts. The salt was open to atmosphere without acover. A sample panel #2 of 908 nickelsteel was suspended from a wirethrough a hole punched in its upper section, and immersed in thecatholyte for fifteen minutes, then quenched in cold water to removeadhering salt and to cool the panel, and finally immersed in a fifteen(15 percent nitric acid (by weight) pickling bath at one hundred andsixty (160) degrees Fahrenheit for three (3) minutes. The sample of 908was then rinsed in cold, followed by hot water, and inspected forevaluating the results. It was rated to be descaled ninety (90) percenton the front face and one hundred (100) percent on the reverse surface.A further test on panel #1 under these conditions yielded similarresults.

EXAMPLE 2 To the conditions existing for Example 1 was added a floatingcover on the catholyte to minimize atmospheric oxidation. A sample panel#3 of 908 nickel-steel was immersed for fifteen 15) minutes in the melt,water quenched, pickled three (3) minutes in nitric acid of Example 1,rinsed and dried. By inspection, the front face was ninety (90) percentand reverse face one hundred (100) percent descaled. Other panels testedyielded similar results.

EXAMPLE 3 To the conditions existing for Example 2, the Recyclotroncurrent wa increased from forty (40) to eighty (80) amperes at 5.6volts. Panel #8 of 908 immersed for fifteen (15 minutes in thecatholyte, quenched and treated in nitric acid as in Example 2, yieldedresults of sixty (60) to one hundred (100) percent descaled on front andreverse faces repsectively.

EXAMPLE 4 To the conditions existing for Example 3, the Recyclotroncurrent was raised from eighty (80) amperes to one hundred and twenty(120') amperes at 6.9 volts. Initial sample Panels #13 and #15 of 908processed as described in Example 3, yielded better-than-average resultsranging between ninety-five (95) and one hundred (100) percentdescaling. As the electrolyte was maintained under these operatingconditions, further tests on panels of 908 nickel-steel, panels #16, #17and #18, yielded consistently perfect results, with descaling rated atone hundred (100) percent on both faces.

10 EXAMPLE 5 With the conditions existing under Example 4, theRecyclotron current was reduced from one hundred and twenty 120) toeighty amperes, and tests were conducted as in Example 3 on panels #19,#20 and #21 of 908. All the results were consistently excellent, allpanels rating at one hundred percent descaled on both faces.

EXAMPLE 6 With the conditions existing under Example 5, the Recyclotroncurrent was reduced from eighty (80) amperes to zero (0) amperes byshutting the system down. The only current still remaining was thatflowing in the passivating circuit. Panels #22 through #26 of 908 wereprocessed as before in Example 3, and examined. Results wereconsistently bad, descaling ranging between two (2) percent to fifteen(15 percent.

EXAMPLE 7 With the conditions existing under Example 6, the Recyclotroncurrent was turned on, raising it from zero (0) to eighty (80) amperes,and the temperature of the melt was increased from seven hundred andtwenty-one (721) degrees Fahrenheit to nine hundred and twenty-one (921)degrees Fahrenheit. Under these new conditions, panels of 908nickel-steel were processed as before in Example 3. Initially, as thereducing chemicals werestill being created in the catholyte, results onpanels #27 through #30 were eighty (80) to ninety-eight (98) percentdescaled. Within two (2) hours, under the same conditions, however, onehundred (100) percent descaling was achieved on both faces of 908 panels#31 and #32.

EXAMPLE 8 With the conditions existing under Example 7, the Recyclotroncurrent was reduced from eighty (80) to forty (40) amperes, and thetemperature was allowed to drop slightly from nine hundred andtwenty-one (921) to nine hundred (900) degrees Fahrenheit. Under thesenew conditions, panels #33 through #35 of 908 processed as in Example 3were all perfectly descaled and rated at one hundred-one hundred (100100) percent descaled on both front and reverse faces, respectively.

EXAMPLE 9 With the conditions existing as in Example 8, the electrodeswere moved from a distance eight and one-half (8 /2) inches apart, to anew position where they were four and three-quarter inches apart. Underthese new conditions, panels #36 through #40 of 908 nickel-steel wereprocessed as in Example 3, with perfect results; all panels rated wereone hundred 100-) percent descaled on both sides.

EXAMPLE 10 With identical conditions existing as in Example 9, panel #41of 908 nickel-steel was processed in the catholyte for ten (10) minutes,then pickled for five (5) minutes in a ten (10) percent nitric acid atone hundred and sixty degrees Fahrenheit, rinsed and dried. Examinationof panel #41 was near-perfect at ninety-nine (99) percent descaled onthe front face and one hundred (100) percent on the reverse face.

EXAMPLE 11 Identical salt conditions as existing in Example 9, a panel#42 of 908 nickel-steel was processed in the catholyte for only five (5)minutes, then pickled for three (3) minutes in the ten (10) percentnitric acid at one hundred and sixty (160) degrees Fahrenheit, rinsedand dried. Panel #42 was rated ninety-nine (99) percent descaled on thefront face and one hundred (100) percent on the reverse face.

1 1 EXAMPLE 12 Under identical salt conditions as existing in Example 9,a panel #43 of 908 nickel-steel was processed in the anolyte for fifteen(15) minutes, which after quenching, was pickled for three (3) minutesin ten percent nitric acid at one hundred and sixty (160) degreesFahrenheit, rinsed and dried. Panel #43 was rated atninetynine-ninety-nine (9999) percent descaled, front and rear faces.

EXAMPLE 13 With conditions existing under Example 9, only thetemperature was lowered from nine hundred (900) degrees Fahrenheit toseven hundred and ninety-eight (798) degrees Fahrenheit. Under thiscondition, a panel #45 of 908 nickel-steel was processed in thecatholyte for fifteen minutes, water-quenched, then pickled for three(3) minutes in the acid of Example 12. Panel #45 was rated at onehundred-one hundred (100-100) percent descaled on both front and reversefaces.

EXAMPLE 14 With conditions existing under Example 13, the temperaturewas again lowered from seven hundred and ninety-eight (798) to sixhundred and ninety-five (695) degrees Fahrenheit. Under this condition,a panel #46 of 908 nickel-steel was processed exactly as in Example 13.Panel #46 was rated at one hundred-one hundred (100-100) percentdescaled on both front and reverse faces.

Just a few words on the interpretation of these fourteen (14) examples.Initially, conditions existing in the melt were unsatisfactory todescale the tough 908 nickel-steel; this was the period of electrolyticdehydration of the traces of moisture present in the salt, undoubtedlyexisting during the periods of Examples 1, 2 and 3. During the operatingperiod of Example 4, early tests (panels #13 and #15) were somewhatimperfect, due primarily to the fact that the dehydrated bath was nowbeing supplied with suificient reducing chemicals by the Recyclotroncurrent. As the concentration of reducing agents built up in thecatholyte, however, later tests (panels #16, #17 and #18) yieldedperfect descaling of 908 nickel-steel. Even reducing the Recyclotroncurrent for Example 5 continued to yield perfect results on descaling908 nickel-steel. Shutting the Recyclotron current off, however, as inExample 6, allowed all the reducing agents to quickly revert to theirhigher oxidation states, and panels of 908 processed during this periodwere definitely not descaled. When the Recyclotron current was restored,however, only enough time transpired to re-create the reducing agents,as the melt had already been previously dehydrated. The conditions ofExample 7 depict this condition as well as the effect of raising thetemperature. Once the reducing chemicals are electrolytically createdand maintained, the amount of power input will depend on the amount ofdescaling work the bath is expected to perform. In Example 8, theRecyclotron current was again reduced simultaneously with lowering thetemperature, and it continued to descale 908 panels perfectly. Movingthe electrodes closely together, as in Example 9, did not adverselyaffect the functioning of the descaling bath, and in fact cuttingprocessing times gradually from fifteen (15) to five (5) minutes in thesalt and pickling the panels in weaker nitric acid as in Example 10 andExample 11 still continued to achieve remarkable descalingeffectiveness. Even enough of the reducing chemicals migrated throughthe diaphragm screen into the anolyte to effectively descale 908nickel-steel, as in Example 12. Continued lowerings of the temperatureas in Example 13 and Example 14 did not appreciably reduce the abilityof the catholyte to descale 908.

Further examples will illustrate the remarkable ability of the system ofthis invention to descale a variety of stainless steels. These steelsare common enough to be standardized in composition ranges and arelisted by both 12 SAE and A151 (Society of Automotive Engineers andAmerican Iron and Steel Institute) standards steels composition lists.

The suffixes HRN, ERA and BA below noted designate Hot-Rolled NaturalSheet, Hot-Rolled and Annealed Sheet, and Box-Annealed Sheetrespectively.

Stainless steels tested were the following:

Type 302 HRN Type 302 HRA Type 309 HRN Type 309 HRA Type 321 HRN Type321 HRA Type 410 HRN Type 410 BA Type 430 HRN Type 446 HRN Type 446 HRAEXAMPLE 15 A salt composition A as in Example 1 supra, existing underthe conditions of Example 9 supra. All eleven (11) types and conditionsof stainless steel scaled panels were immersed in the catholyte forfifteen (15 minutes, then water-quenched. According to the alloy, eachpanel was then individually subjected to its own special pickling acidsequence. The following is a tabulation of the pickling acids andsequence, and the descaling results:

10% 10%-2% Percent Descaled Stainless Steel 10% H01 HNO; BNO;-

Type F), F HF mm. min. (120? F.) Front Reverse min.

5 100 100 3 100 100 5 100 100 4 100 99 2 100 100 5 100 100 2 100 98 5100 100 4 100 100 2 100 100 446HRA 4 100 09. 0

EXAMPLE 16 Percent Desealed Stainless Steel Type Front Reverse 302 H RN446 HRA EXAMPLE 17 With salt and conditions existing under Example 13supra, the eleven (11) types and conditions of stainless steel scaledpanelswere processed in the catholyte for fifteen (15 minutes. Afterwater quenching, they were pickled, according to alloy and scalecondition, as in Example 15 The front faces of all panels were onehundred (100) perwnt descaled; the reverse faces of all panels were onehundred (100) percent descaled with two (2) exceptions: 410 HRN wasninety-eight (98) percent and 309 HRA was ninety-nine (99) percent.

EXAMPLE 18 With salt and conditions existing under Example 13 andExample 17 supra, the eleven (11) types of stainless steel scaled panelswere subjected to the action of the anolyte for fifteen 15) minutes andthen water quenched. They were acid pickled as in Example 15. The frontand reverse faces of all panels were one hundred-one hundred 100-100)percent descaled with the following exceptions: 410 HRN was rated onehundred-ninety-eight (100-98) and 446 HRA was ratedninety-nine-ninetyeight (99-98) percent descaled on front and reversefaces respectively.

EXAMPLE 19 With the molten electrolyte and conditions existing as underExample 14 supra, the eleven (11) types and conditions of stainlesssteel scaled panels were subjected to the reducing action of thecatholyte for fifteen (15) minutes. After water quenching, theindividual panels were then pickled according to the time cycles andsequences of Example 15. The results were as follows: all panels wereone hundred-one hundred (ll00) percent descaled on both front andreverse faces with the exception of Type 446 HRA, which was ratedninetynine-ninety-eight (99-98) percent descaled on front and reversefaces respectively.

EXAMPLE 20 Under the same identical conditions as exist in Example 19supra, the eleven (11) types and conditions of stainless steel scaledpanels were subjected to the action of the anolyte for fifteen (15)minutes. After water quenching and acid pickling according to that ofExample 15, all but three (3) panels were perfectly descaled. The three(3) were as follows: Type 410 HRN was one hundred-ninety-nine (100-99);Type 446 was ninety-fiveninety (95-90); and Type 309 HRA wasninety-fifty (90-50) percent descaled on front and reverse faces.

The first twenty (20) examples cited supra were descaling testsperformed using a design of a Recyclotron as indicated in FIGURE I,which is the simplest of the possible designs. From a commercial pointof view, the fundamental design of FIGURE II is preferred because of itsgreater adaptability to any presently-existing fused salt furnaces.Without any physical changes whatsoever of existing equipment, theinstallation of a Recyclotron incorporating the basic features of FIGUREII automatically converts such equipment to the reducing descalingsystem of the present disclosure (this assumes, of course, that the potis charged with the proper salt composition as disclosed above). Example21 through Example 28 inclusive make use of equipment adapted accordingto the basic design features outlined in FIGURE II.

EXAMPLE 21 A steel pot incorporated in an electrically-heated andautomatically-controlled furnace, approximately three (3) feet long bythree 3) feet wide by two and one-half (2%) feet deep was charged withtwo thousand, one hundred and sixty (2,160) pounds of technical gradecaustic soda based on its dry weight, and the temperature raised to thefusion point. When the NaOH was in the fused, molten condition at aboutsix hundred and fifty (650) degrees Fahrenheit, two hundred and forty(240) pounds of anhydrous sodium sulfate was added, which then dissolvedto form a composition B comprising two thousand, four hundred (2,400)pounds of total salt in the percentage ratio of ninety (90) percent NaAHand ten percent sodium sulfate. When the temperature of this meltreached seven hundred (700) degrees Fahrenheit, a Recyclotron unit ofthe general design features of FIGURE II was lowered into the pot. ThisRecyclotron unit consisted of a steel housing approximately twenty (20)inches by twenty (20) inches by seven (7) inches, incorporating a steelcombination baffle-diaphragm of twenty (20) inches by twenty (20)inches, in the lower half of which is positioned a twelve (12) inch byfourteen (14) inch diaphragm screen. Within the steel housing waspositioned a nickel anode means comprising four hundred and eighty (480)square inches of immersed surface area. (The anode comprises a pluralityof vertically-suspended slats to achieve a relatively high surfacearea.) A copper cathode means, having a submerged sheet portion twelve(12) inches by fourteen (14) inches, was positioned in the pot,externally of the housing, and immediately adjacent to and parallel withthe outer face of the diaphragm screen.

A passivating circuit was connected to the pot, the housing means of theRecyclotron, the combination bafllediaphragm means, and was held atseventeen (17) amperes at 3.3 volts. The function of the passivatingcircuit, as indicated above, is to protect these listed elements in thesystem from the detrimental corrosion that would otherwise exist.

The Recyclotron current was initially established at approximately twohundred (200) amperes at 4.7 volts for a period of three (3) days forthe purpose of electrolytic dehydration of the salt bath. The currentwas then increased to two hundred and seventy (270) amperes at six (6.0)volts for establishing the operating conditions in the bath.

The salt temperature was maintained at eight hundred (800) degreesFahrenheit. A floating cover was added to the surface of the catholyte.

Three 3) panels of 908 nickel-steel, each eighteen 18) inches byeighteen (18) inches, were simultaneously immersed in the catholyte ofthis system for a period of twenty (20) minutes, then water-quenched.This was subsequently followed by pickling for three (3) minutes in ten(10) percent H 50 (at one hundred and seventy-five (175) degreesFahrenheit), two (2) minutes in ten (10) percent HNO (one hundred andsixty (160) degrees Fahrenheit), and two (2) minutes in a mixed acidcomprising ten (10) percent HNO with two (2) percent HF (at one hundredand twenty (120) degrees Fahrenheit). After rinsing and drying,examination of the 908 nickelsteel panels revealed that they were onehundred-one hundred (100-100) percent descaled on both faces.

EXAMPLE 22 Under the conditions of Example 21, a scaled panel of fifty(50) percent nickel-fifty (50) percent ir-on alloy, was immersed in thecatholyte for thirty (30) minutes, water-quenched and pickled asfollows: two (2) minutes in the previously mentioned (Example 21) Hfollowed by one and one-half (1 /2) minutes in the previously mentioned(Example 21) HNOg-HF acid mixture. The panel was one hundred percentdescaled on both faces.

EXAMPLE 23 Under the conditions of Example 21, immersed in the catholytefor thirty (30) minutes was a scaled panel of high nickel alloy of thefollowing approximate composition: fifty-one (51) percent Ni, nineteen(19) percent Cr, eleven (11) percent Co, ten (10) percent M0, 3.2percent Ti, four (4.0) percent Fe, 1.6 percent A1, 0.3 percent Mn. 0.1percent C, and 0.005 percent B. The ten (10) inch by six and one-half (6/2) inch panel was water-quenched, acid-treated under the sameconditions and in the same manner as the panel treated in Example 22.This panel upon inspection, was indicated to be one hundred (100)percent descaled on both sides.

EXAMPLE 24 Under the conditions of Example 21, a scaled panel of Type304 stainless steel, six and one-half (6 /2) inches by sixteen (16)inches, was immersed in the catholyte for a total of five (5) minutesand then quenched in water. The

panel was then acid-treated for three (3) minutes in ten (10) percent H80 (at one hundred and fifty-eight (158) degrees Fahrenheit), followedby three (3) minutes. in ten (10) to two (2) percent HNO -HF (at onehundred and twenty (120) degrees Fahrenheit). The panel, upon rinsingand drying, was completely (one hundred (100) percent) descaled on bothsides.

EXAMPLE 25 Under the conditions of Example 21, a hot-rolled and annealedscaled panel of Type 316 stainless steel, approximately nine andone-half (9 /2) inches by fifteen (15) inches was immersed in thecatholyte for a period of twenty (20) minutes and then water-quenched.The panel was then pickled for five minutes in ten percent H 50 (at onehundred and fifty-eight (158) degrees Fahrenheit) followed by three (3)minutes in the HNO HF mixed acid of Example 21. After rinsing anddrying, the Type 316 panel processed as above was examined and rated tobe one hundred (100) percent descaled on both surfaces.

EXAMPLE 26 Under the conditions of Example 21, a low-nickel alloy steelpaneL termed A181 4335, approximately twelve (12) inches by fifteeninches, was immersed in the catholyte for a period of five (5) minutesfollowed by a water quench. After pickling for ninety (90) seconds inthe ten (10) percent H SOL, of Example 25, the panel was rinsed in coldwater, and then dried. Although covered with a light smut, the panel wasrated as being fully one hundred (100) percent descaled on both sides.

EXAMPLE 27 Under the conditions of Example 21, a box-annealed sheet ofType-410 stainless. steel, approximately twelve (12) inches by sixteenand one-half (116 /2) inches, was immersed in and subjected to thereducing action of the catholyte for a period of five (5) minutes. Thesheet was quenched in cold water and followed by pickling for thirty(30) seconds in ten 10) percent H 50 under the conditions and manner ofExample 25, followed by one (1) minute in ten (10) percent HNO at onehundred and sixty (160) degrees Fahrenheit. After rinsing and drying,the sheet of Type 410 was obviously clean and one hundred (100) percentscale-free on both faces.

EXAMPLE 28 EXAMPLE 29 A steel pot sixteen (16) inches by sixteen (16)inches by twelve (12) inches deep, fitted with slots for holding andpositioning the nickel diaphragm screen twelve (12) inches by fifteenand one-half (15 /2) inches, was charged with a salt composition C whichcomprised sixteen and one-half (16 /2) percent of anhydrous sodiumsulfate and eighty-three and one-half (83 /2) percent technical gradeNaOH (based on one hundred and twenty-five (125) pounds total dry weightof the components). This mixture is closely equivalent to the eutecticcomposition of these two (2) components as determined by a series offreezing point determinations carried out over a large range of sulfatepercentages in fused sodium hydroxide. The furnace Was controlled tomaintain the fused salt mixture at eight hundred (800) degreesFahrenheit. A

four (4) inch by five (5) inch submerged copper cathode means and a four(4) inch by five (5) inch submerged nickel anode means was positioned oneither side of the centrally-positioned diaphragm means. A passivatingcircuit was employed and connected to the steel pot and to thediaphragm, with the current set and maintained at two (2) amperes at two(2) volts. The Recyclotron current flowing through the main electrodeswas established at sixty ('60) amperes at 4.2 volts.

Salt composition C was electrolyzed for forty-eight (48) hours underthese conditions for dehydration and to create the reducing agents inthe catholyte. At this point, a scaled panel of 908 nickel steel, three(3) inches by six (6) inches, was immersed in the catholyte for a totalof fifteen (15 minutes. After quenching in water, the panel wasprocessed for three (3) minutes in fifteen (15) percent HNO (at onehundred and sixty (160) degrees Fahrenheit) rinsed and dried. The three3) inches by five (5) inches nickel steel panel was completely strippedof its tough oxide scale, leaving one hundred percent descaled on bothsides.

EXAMPLE 30 EXAMPLE 31 Under the conditions of Example 29, a six (6) inchby six (6) inch panel of scaled titanium of commercial purity wasimmersed in the catholyte for thirty (30) seconds, then water-quenched.The panel was then subjected to a five (5) second flash dip in ten (10)to two (2) percent HNO -HF mixture at one hundred and twenty degreesFahrenheit, rinsed and dried. The panel of titanium was very bright,being one hundred (100) percent descaled on both surfaces.

EXAMPLE 32 Under the conditions of Example 29, a panel of a titaniumalloy scaled at one thousand eight hundred (1,800)

.degrees Fahrenheit was immersed in the catholyte for a period of threeand one-half (3%) minutes. The approximate composition of the alloy was72.5 percent Ti, thirteen (13) percent V, eleven (11) percent Cr andthree (3) percent Al. After water quenching, the panel was pickled fortwenty (20) seconds in the HNO -HF acid mixture referred to in Example31. After rinsing and drying, the 13-11-13 titanium alloy was rated tobe one hundred (100) percent descaled on both sides.

EXAMPLE 33 Under the conditions of Example 29, a scaled panel of Type302 stainless steel was immersed in the catholyte for ten (10) minutes,then water-quenched. This was followed by acid pickling in fifteen (15)percent HNO (at one hundred and sixty degrees Fahrenheit) for four (4)minutes, then in ten (10) percent to two (2) percent HNO -HF (at onehundred and twenty (120) degrees Fahrenheit) for thirty (30) seconds.After rinsing and drying, the panel of Type 30-2 was rated to be onehundred (100) percent descaled and bright on both faces.

EXAMPLE 34 Under the conditions of Example 29, a scaled panel of atypical stainless steel was immersed in the catholyte for a period oftwo (2) minutes. This alloy had the proxi mate composition oftwenty-seven (27) percent Ni, twenty (20) percent Cr, two and one-half(2 /2) percent Mo, three (3) percent Cu and the remainder Fe. Afterwater quenching, the panel was pickled for one (1) minute in ten (10)percent HCl (one hundred and fifty (150) degrees Fahrenheit) followed byone and one-half (1 /2) minutes in ten (10) percent to two (2) percentHNO -HF (one hundred and twenty (120) degrees Fahrenheit). The panel wasdescaled one hundred (100) percent on both sides.

EXAMPLE 35 Under the conditions of Example 29, a six (6) inch by six (6)inch by one-quarter inch plate of scaled Type 430 stainless steel wasimmersed in the catholyte for a total time of one (1) minute. Afterquenching in cold water, the plate was pickled for one (1) minute infifteen (15) percent HNO (one hundred and sixty (160) degreesFahrenheit) followed by a ten (10) second bright dip in ten (10) percentto two (2) percent HNO -HF (one hundred and twenty (120) degreesFahrenheit), rinsed and dried. The type 430 plate was one hundred (100)percent descaled on both surfaces.

The above-defined composition can be easily adapted also for use as ahome or other structure heating system. The sodium sulfate-sodiumhydroxide composition can be located in a furnace or other containingmeans having positioned therein a composition heating means; such ascoils, burners, etc. When required the bath would be heated therebystoring heat or energy which may be drawn upon over a period of time.The passivating circuit described in this disclosure is ideally adaptedfor use in this heating system, thereby providing a minimum ofmaintenance.

Although this invention has been illustrated and defined herein in termsof the above examples and accompanying drawings, it is to be understoodthat these are by no means all inclusive. Various modifications to theinvention herein set out *will suggest themselves to those skilled inthe art. These are intended to be comprehended within the spirit of thisinvention.

We claim:

1. A process for producing a reducing bath for the descaling of met-a1oxides on the surface of a metal article wherein the reducing bath isformed in a metal container having therein a source of positive andnegative current separated from each other by a diaphragm therebyforming an anode zone and a cathode zone comprising im-- posing adecomposition voltage through a molten salt mixture within saidcontainer, said molten salt mixture being comprised of a substantiallyanhydrous mixture of at least about three percent alkali-metal sulfatein a major proportion of alkali-metal hydroxide, reducing saidalkali-metal sulfate, maintaining the reduced alkalimetal sulfate insaid cathode zone, thereby producing a reducing bath of alkali-metalhydroxide and reduced alkali-metal sulfate selected from the groupconsisting of alkali-metal sulfites, alkali-metal dithionites,alkalimetal thiosulfates, alkali-metal pyrosulfites, alkali-metalsulfides and mixtures thereof.

2. The process of claim 1 wherein said alkali-metal sulfate is sodiumsulfate and said alkali-metal hydroxide is sodium hydroxide.

3. A process for the descaling of metal oxides on the surface of a metalarticle in a reducing bath wherein the in a source of positive andnegative current separated from each other by a diaphragm therebyforming an anode Zone and a cathode zone comprising imposing adecomposition voltage through a molten salt mixture within saidcontainer, said molten salt mixture being comprised of a substantiallyanhydrous mixture of at least three percent alkali-metal sulfate in amajor proportion of alkali-metal hydroxide, reducing said alkali-metalsulfate thereby producing a reducing bath of alkali-metal hydroxide andreduced alkali-metal sulfate selected from the group consisting ofalkali-metal sulfites, alkali-metal dithionites, alkali-metalthiosulfates, alkali-metal pyrosulfites, alkali-metal sulfides andmixtures thereof in said cathode zone, passing into said cathode zone ofsaid molten salt mixture containing said reduced alkali-metal sulfate, ametal article having on its surface metal oxides, reacting said metaloxides with said reduced alkali-metal sulfates, thereby reducing saidoxides and subsequently withdrawing said metal article from said moltensalt mixture.

4. The process of claim 3 wherein said molten salt mixture is maintainedat a temperature of about 700 to 900 degrees Fahrenheit and wherein thecurrent density is maintained in the range of about 0.5 to 3.5 amperesper square inch of cathode area.

5. The process of claim 3 wherein on removing said metal article fromsaid cathode zone, said metal article is quenched with cold water,immersed in an acid pickling solution and subsequently rinsed withwater.

6. A process adapted to protect the component elements of asubstantially anhydrous electrochemical descaling system from corrosion,said descaling system being a molten bath comprising a major proportionof an alkali- .metal hydroxide in a metal container having therein anodeand cathode means comprising electrically connecting said anode andcathode means of an electrochemical descaling system to a primary sourceof direct electrical current, electrically connecting the elements to beprotected to a positive pole of a secondary source of direct electricalcurrent, electrically connecting the negative pole of said secondarysource of electrical current to said cathode means, passing a primaryand secondary electrical current through said cathode to said anodes,and maintaining said secondary current to said elements to be protectedsubstantially less than the primary current to said anode means of saidelectrochemical descaling system.

References Cited by the Examiner UNITED STATES PATENTS 472,691 4/1892Benjamin 204145 2,311,099 2/1943 Tainton 204 145 2,349,662 5/1944Keating 204 252 2,448,262 8/1948 Gilbert 204 145 2,678,289 5/1954 Nobleell a1. 204 145 2,834,728 5/1958 G allone 204 147 2,847,374 8/1958Webster et al. 204 -145 2,848,411 8/1958 Hartzell 204 290 2,860,10011/1958 Krzyszkowski 204 252 2,890,157 6/1959 Raetzsch 204 147 2,909,47110/1959 Nies 204 147 2,929,769 3/1960 Newell 204 290 2,936,278 5/1960Shoemaker of al. 204 145 JOHN H. MACK, Primary Examiner. reducing bathis formed in a metal container having there- 60 P. SULLIVAN, R. L.GOOCH, R. MIHALEK,

Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,293,159 December 20, 1966 Matthew Mekjean et al.

rror appears in the above numbered pat- It is hereby certified that eetters Patent should read as ent requiring correction and that the saidL corrected below.

Column 1, line 34, after "not" insert only column 2,

" read Electrolytic line 60,

line 28, for "Electrolyte for "+S O read +5 0 column 9, line 61, for

"repsectively" read respectively column 13, line 70, for "NaAH" readNaOH column 14, line 64, for "Mn." read Mn, column 15, line 49, for"(16)" read (l5) Signed and sealed this 3rd day of December 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A PROCESS FOR PRODUCING A REDUCING BATH FOR THE DESCALING OF METALOXIDES ON THE SURFACE OF A METAL ARTICLE WHEREIN THE REDUCING BATH ISFORMED IN A METAL CONTAINER HAVING THEREIN A SOURCE OF POSITIVE ANDNEGATIVE CURRENT SEPARATED FROM EACH OTHER BY A DIAPHRAGM THEREBYFORMING AN ANODE ZONE AND A CATHODE ZONE COMPRISING IMPOSING ADECOMPOSITION VOLTAGE THROUGH A MOLTEN SALT MIXTURE WITHIN SAIDCONTAINER, SAID MOLTEN SALT MIXTURE BEING COMPRISES OF A SUBSTANTIALLYANHYDROUS MIXTURE OF AT LEAST ABOUT THREE PERCENT ALKALI-METAL SULFATEIN A MAJOR PROPORTIONOF ALKALI-METAL HYDROXIDE, REDUCING SAIDALKALI-METAL SULFATE, MAINTAINING THE REDUCED ALKALIMETAL SULFATE INSAID CATHODE ZONE, THEREBY PRODUCING A REDUCING BATH OF ALKALI-METALHYDROXIDE AND REDUCED ALKALI--METAL SULFATE SELECTED FROM THE GROUPCONSISTING OF ALKALI-METAL SULFITES, ALKALI-METAL DITHIONITES,ALKALIMETAL THIOSULFATES, ALKALI-METAL PYROSULFITES, ALKALI-METALSULFIDES AND MIXTURES THEREOF.
 3. A PROCESS FOR THE DESCALING OF METALOXIDES ON THE SURFACE OF A METAL ARTICLE IN A REDUCING BATH WHEREIN THEREDUCING BATH IS FORMED IN A METAL CONTAINER HAVING THEREIN A SOURCE OFPOSITIVE AND NEGATIVE CURRENT SEPARATED FROM EACH OTHER BY A DIAPHRAGMTHEREBY FORMING AN ANODE ZONE AND A CATHODE ZONE COMPRISING IMPOSING ADECOMPOSITION VOLTAGE THROUGH A MOLTEN SALT MIXTURE WITHIN SAIDCONTAINER, SAID MOLTEN SALT MIXTURE BEING COMPRISED OF A SUBSTANTIALLYANHYDROUS MIXTURE OF AT LEAST THREE PERCENT ALKALI-METAL SULFATE IN AMAJOR PROPORTION OF ALKALI-METAL HYDROXIDE, REDUCING SAID ALKALI-METALSULFATE THEREBY PRODUCING A REDUCING BATH OF ALKALI-METAL HYDROXIDE ANDREDUCED ALKALI-METAL SULFATE SELECTED FROM THE GROUP CONSISTING OFALKALI-METAL SULFITES, ALKALI-METAL DITHIONITES, ALKAI-METALTHIOSULFATES, ALKALI-METAL PYROSULFITES, ALKALI-METAL SULFIDES ANDMIXTURES THEREOF IN SAID CATHODE ZONE, PASSING INTO SAID CATHODE ZONE OFSAID MOLTEN SALT MIXTURE CONTAINING SAID REDUCED ALKALI-METAL SULFATE, AMETAL ARTICLE HAVING ON ITS SUFACE METAL OXIDES, REACTING SAID METALOXIDES WITH SAID REDUCED ALKALI-METAL SULFATES, THEREBY REDUCING SAIDOXIDES AND SUBSEQUENTLY WITHDRAWING SAID METAL ARTICLE FROM SAID MOLTENSALT MIXTURE.
 6. A PROCESS ADAPTED TO PROTECT THE COMPONENT ELEMENTS OFA SUBSTANTIALLY ANHYDROUS ELECTROHEMICAL DESCALING SYSTEM FROMCORROSION, SAID DESCALING SYSTEM BEING A MOLTEN BATH COMPRISING A MAJORPROPORTION OF AN ALKALIMETAL HYROXIDE IN A METAL CONTAINER HAVINGTHEREIN ANODE AND CATHODE MEANS COMPRISING ELECTRICALLY CONNECTING SAIDANODE AND CATHODE MEANS OF AN ELECTROCHEMICAL DESCALING SYSTEM TO APRIMARY SOURCE OF DIRECT ELECTRICAL CURRENT, ELECTRICALLY CONNECTING THEELEMENTS TO BE PROTECTED TO A POSITIVE POLE OF A SECONDARY SOURCE OFDIRECT ELECTRICAL CURRENT, ELECTRICALLY CONNECTING THE NEGATIVE POLE OFSAID SECONDARY SOURCE OF ELECTRICAL CURRENT TO SAID CATHODE MEANS,PASSING A PRIMARY AND SECONDARY ELECTRICAL CURRENT THROUGH SAID CATHODETO SAID ANODES, AND MAINTAINING SAID SECONDARY CURRENT TO SAID ELEMENTSTO BE PROTECTED SUBSTANTIALY LESS THAN THE PRIMARY CURRENT TO SAID ANODEMEANS OF SAID ELECTROCHMICA DESCALING SYSTEM.